The power requirements of electrical systems are becoming ever more demanding. To maximize energy efficiency, power density, and system serviceability, the power system designer is being asked to provide increased functionality and improved performance at minimal cost. As a result, power supplies and their controllers are becoming increasingly complex.
One of the trends challenging designers is the requirement for more regulated output voltages within the same system. A typical battery powered personal digital assistant (PDA) may reasonably be expected to provide four or more different voltages, each with dramatically different dynamic requirements. One supply may service the CPU, another, the display, another the touch screen and another an RF transceiver. In the case of a multi-output power supply, i.e., a power supply providing multiple regulated output voltages, the designer is challenged not only by the problems posed by the control of multiple power stages, but also by the problems of interactions among controllers. Existing tools and techniques for designing single-output power supplies do not address these challenges.
Another trend is the requirement for systems to operate with multiple input power sources. For example, a device may at times be powered by batteries with one range of input voltages and at other times be line powered with a different range of input voltages. In the case of large systems, the use of uninterruptible backup power supplies is increasingly common. In the case of a multi-input power supply, i.e., a power supply incorporating two or more alternate input power sources, the designer is challenged not only by the requirement for “graceful” switching between or among input power sources, but also by the widening range of input voltages to the power stages.
Still another trend is the widespread adoption of “distributed” power systems that allow, for example, the modular expansion of large electronic systems through “hot swapping” of subsystems. These systems generally involve a hierarchy of different power supplies, with one or more power supplies providing power to others. In the case of distributed power systems, the system designer is challenged to implement a modular, yet cost-effective power system architecture. To help designers implement this architecture, a new category of programmable devices, known as power management devices, has evolved. These devices, capable of managing the operation of multiple power supplies, have found use in battery-powered systems as well.
In the case of battery-powered systems, the continued pressure on the system designer to reduce parts count, space, weight and cost is driving an industry trend toward combining multiple controllers within a single integrated circuit. Such a device is referred to as a multi-output controller or multi-controller. But there are many barriers to achieving this level of integration.
One major barrier to integration is the large number of power supply topologies, including: buck, boost, buck-boost, fly-back, fly-forward, isolated, non-isolated, DC to DC, DC to AC, and AC to AC, etc. In addition to the large number of topologies, the control strategies employed to control these topologies are likewise numerous, supporting a variety of operating modes including continuous conduction, discontinuous conduction, critically discontinuous conduction, and others. Historically, the economics of the controller marketplace has mitigated in favor of topology-specific (and even control-strategy-specific) controllers, implemented with analog circuitry. Carrying this analog theme forward, a few commercial multi-controllers, realized essentially by integrating an application-specific ensemble of topology-specific controllers, have been introduced to the marketplace. Broad acceptance of such devices will happen slowly as different topology (and control strategy) combinations and permutations are introduced. This proliferation of devices, however, becomes a barrier of its own, as the rapidly growing number of different device types will create substantial manufacturing disadvantages for both customers and vendors.
Furthermore, the barriers to integration are not limited to those implicit in combining and permuting controllers. In fact, in very high volume applications, it is often desirable to integrate the power supply controller with other elements of the system into an application specific integrated circuit (ASIC). A barrier to this is that controllers have historically been designed using analog circuit techniques, which are generally difficult to integrate into system-level ASIC design methodologies that are primarily digital in nature. And this problem is further compounded by a general lack of available personnel that combine power systems and mixed-signal silicon design expertise.
A promising trend in power supply controller design is the replacement of analog control loops with conventional digital logic. The application of digital logic further provides the foundation for a flexible controller, that is a controller that can be synthesized from a flexible controller template to control any topology using any applicable control strategy, substantially overcoming the controller integration-proliferation barriers.
With modern semiconductor geometries, the impact of a small number of unused gates in a multi-topology controller is negligible as other factors dominate the cost, e.g., packaging, etc. Further, by allocating a portion of the memory incorporated in the flexible controller template for the purpose of enabling user-programmability, user-configurable multi-controllers, capable of controlling different topologies in different combinations are realizable. The flexible controller then becomes the building block enabling the realization of integrated multi-controllers, including user-configurable multi-controllers, capable of serving a broad spectrum of applications. With digital logic, the circuitry of the controller is more easily realized using the design techniques of modern ASICs, overcoming the ASIC integration barrier as well. Only a limited number of analog cell types (such as a voltage comparator, reference voltage generator, amplifiers, A/D and D/A converters, etc.) are required to implement the controller. Design of these cells is relatively easy and requires no special knowledge of power systems or special manufacturing processes. Indeed, many ASIC design systems already have the requisite cells in their libraries.
The lack of personnel with the required power systems and mixed-signal design experience remains as a barrier. Consequently, there is a need to have computer-aided tools for the design of multi-input, multi-output power supplies and especially for the design of multi-controllers, for systems large (distributed) and small (battery-powered). These tools should address the requirements for multi-controllers, whether the requirements be for a hierarchy of inter-communicating controllers or multi-controllers, or for a standalone multi-controller, or for a multi-controller integrated with other system elements using standard logic processes.